Underdrive Pullies

[Sludgy]

Radiator fans and cooling pumps drag power from the engine according to the CUBE of their speed. Halving their speed means 1/8 of the drag. Doubling the speed means 8 times as much drag on a race engine, so high RPMs fans and pumps hurt power for racers and hurt our economy.

Underdrive pulleys saves substantial HP for racers, but the effect is a lot less for us gas pinchers that keep engine RPMs down anyway. Even so, underdrive pulleys WILL help gas economy though.

The biggest problems with underdrive pulleys are:
1) The car may overheat in hot weather and under hard work. like climbing hills.
2) The alternator needs a minimum RPM to produce enough volts to charge the battery at idle. It could run out of electricity when we're stuck in traffic. Underdrive pulley with a couple of deep cycle batteries could cope with that.

[Matt Timion]

Originally Posted by kickflipjr

Someone tested a saturn stock and a saturn with no crank pully at all and said they only gained 3 hp. They implied that underdrive pullies would provide little if any hp gains.

http://www.teamscr.com/pulleys.htm

I belive this test is totally wrong because the crank pully acts as a blancer for the engine. and a engine with no crank pully would be out of balance.

A very interesting quote from that article, which I think is summed up in a lot of after market gadgets:

Another perspective is that auto manufacturers such as Saturn are always trying to squeeze the last 1/10 of a MPG from their vehicle’s fuel economy estimates. Big dollars and big engineering budgets are dedicated to this task, and you can bet that if any component could be underdriven further (a potential plus for fuel economy) and still meet its performance and durability bogeys, it would have been already.

[MetroMPG]

you can bet that if any component could be underdriven further (a potential plus for fuel economy) and still meet its performance and durability bogeys, it would have been already.

you often hear that statement made about cars in general (if they could make them more efficient, they would have already). seems reasonable. but it's not always true.

cooling systems in particular are designed for "worst case" conditions (e.g. idling in traffic for extended periods in 110 degree heat trying to escape an approaching hurricane). they're not even designed for "average" conditions. the result is that average and "best-case" owners experience lost efficiency through "worst-case" designs that they rarely or never need.

[edit - removed my off-topic rant about aerodynamics being another area where car companies aren't offering efficient choices. will save that for another day.]

[kickflipjr]

Originally Posted by MetroMPG

i still think it's going to be much lower than 8%.

ooo! surfing around, just found this... some serious underdrive debunking:



so the argument there is the only gains to be had in underdriving are the water pump and the reduced air drag from the alt pulley "fan".

water pumps... the quote above is talking about racing engines (v8's i gather). obviously the size of the gains to be had depend on engine size.

let's do some rough math for my car:

on the teamswift site, one guy replaced his water pump with an electric one that is rated at 1/2 hp, and is stronger than stock. so let's say the stock one costs 1/3 hp. underdriving it by 25% would save me 1/12th of one hp. let's be generous and round it to 1/10th to accound for reduced aero drag on the alt.

1/10th of 1 hp = 75 watts. that won't even power my headlights. yes, it will save fuel, but looks like the savings will be negligible.

continuing further down my very rough calculation road, another figure you see quoted often is road horsepower at highway speed. i.e. i've read several estimates that it takes a modern car between 10-15 hp to cruise at highway speeds on level ground.

assume my car gets 50 mpg (US) at 60 mph and needs 12 hp. if i save 0.1 hp with the underdrive calculations, my highway load drops by 0.83% (0.1 / 12 hp). if the fuel consumption drop is linear, i have just gained 0.42 MPG (50 mpg * 0.83).

suddenly the investment "risk" doesn't look so good (from a strictly fuel saving perspective)...

I was looking around. Underdrivepullies are avalible for the protege for $60, but it looks like I won't be getting one because of this post.

It's good to check on the old threads from time to time.

[brelandt]

Originally Posted by kickflipjr

Someone tested a saturn stock and a saturn with no crank pully at all and said they only gained 3 hp. They implied that underdrive pullies would provide little if any hp gains.

http://www.teamscr.com/pulleys.htm

I belive this test is totally wrong because the crank pully acts as a blancer for the engine. and a engine with no crank pully would be out of balance.

Not always so.....Honda engines are internally balanced. Infact the weight difference between all 4 cylinders are less than 1 gram for Hondas.

Unorthodox racing offers a crank only underdrive kit for Honda engines for this very reason. No need for harmonic balancing.

I susbect this to be true with the Saturn that was tested as well?

[GasSavers_Ryland]

I would think you could be better off finding a more efficent battery, making sure all of your electrical connections are clean, and reducing your electrical loads.
gold electroplated electric contacts? (gold is not a great concuctor in wire form, but doesn't correde to cause resistance)

[CoyoteX]

Underdrive pulleys do help a lot in some situations, my Camaro can eaily pick up .07 seconds at the track with one. I really don't think you could measure the increase on a Metro though. The Camaro has power steering and a/c driven off the belt and is shifting at 6500rpm. An a/c compressor and ps pump do not need to spin that fast so they are just wasting power. Metros and most of the cars here do not have more than the water pump and alternator on their belts so there is not much gain to be had by slowing down the water pump. The alternator gets less efficient as it goes slower so there is no gain to be had there.

If I get around to it I plan on putting an electric water pump on my Metro. It will at best save 1-2hp at over 4000rpm where the water pump is spinning faster than it needs. At idle and under 2000rpm I don't expect a gain other than the faster warmup times and better acceleration not having to spin up the water pump with the motor.

Either way it will be a small gain and more expensive than it is worth money wise, but that has never stopped me from doing stuff before I have already spent more for all the mods total than I will ever get back from saving gas. It is all in the fun of pushing a car to it's limits.

[GasSavers_Ryland]

part of the reason for underdrive pullys on race cars is when you have an engine that normal runs at 3,000 rpm 99% of the time the water pump is running at one speed, now if you are racing, your engine is going to be running much faster 99% of the time (to get more power out of it) so you gear the pully drive system down to run everything else at a speed closer to what they are designed to run at.

[rh77]

Originally Posted by Ryland

I would think you could be better off finding a more efficent battery, making sure all of your electrical connections are clean, and reducing your electrical loads.
gold electroplated electric contacts? (gold is not a great concuctor in wire form, but doesn't correde to cause resistance)

So, I expect better grounding cables would help as well? (I installed a set on a peformance car in the past).

RH77

[green swift]

Originally Posted by MetroMPG

you often hear that statement made about cars in general (if they could make them more efficient, they would have already). seems reasonable. but it's not always true.

cooling systems in particular are designed for "worst case" conditions (e.g. idling in traffic for extended periods in 110 degree heat trying to escape an approaching hurricane). they're not even designed for "average" conditions. the result is that average and "best-case" owners experience lost efficiency through "worst-case" designs that they rarely or never need.

[edit - removed my off-topic rant about aerodynamics being another area where car companies aren't offering efficient choices. will save that for another day.]

The use of an underdrive pulley along with LED lights and I found a pair of driving lights that use only 35 watts each bulb for a total of 70 watts compared to 110 watts for the car lights. These driving lights give off 100 watts of light. So with my LEDs and these driving lights I figure I have reduced my overall wattage by about 106 watts total.This alone will help in the underdrive pulley hands down....Now the cooling issue????